How to parse enum with #[bpaf(external)]?

[potto216]

I am trying to map a command line option to a HciCommand enum but I keep getting an error that the trait bound (): Parser<HciCommand> is not satisfied. What is the best solution?

My code is:

#[derive(Debug, Clone)]
enum HciCommand {
    HciReset,
    HciReadBdAddr
}
    
    static  HCI_RESET_CMD_VALUES: [u8;3] = [0x03, 0x0C, 0x00];
    static  HCI_READ_BD_ADDR_CMD_VALUES: [u8;3] = [0x09, 0x10, 0x00];

impl HciCommand 
{
    fn value(&self) -> &'static [u8] {
        match *self {
            HciCommand::HciReset => &HCI_RESET_CMD_VALUES,
            HciCommand::HciReadBdAddr => &HCI_READ_BD_ADDR_CMD_VALUES,
        }                
    } 
}

impl FromStr for HciCommand {
    type Err = String;
    fn from_str(s: &str) -> std::result::Result<Self, String>
    where
        Self: Sized,
    {
        match s {
            "hci_reset" => Ok(HciCommand::HciReset),
            "hci_read_bd_addr" => Ok(HciCommand::HciReadBdAddr),
             _ => Err("Expected hci_reset|hci_read_bd_addr".to_string()),
        }
    }
}

fn command() -> impl Parser<HciCommand> {    
    short('c')
    .long("command")
    .help("choose between hci_reset or hci_read_bd_addr")
    .argument::<HciCommand>("CMD")
    .to_options()
    .run();
}

#[allow(dead_code)]
#[derive(Debug, Clone, Bpaf)]
#[bpaf(options)]
/// Example for bluetooth low energy controller demo
struct Options {
    #[bpaf(short, long, argument::<String>("DEVICE"), parse(parse_device))]
    /// [vendor]:[product] Open a device with the specified vendor and product ID.
    /// Both IDs are given in hexadecimal.
    device: (u16, u16),

    /// Increase verbosity
    #[bpaf(external)]
    verbose: usize,

    #[bpaf(external)]
    reset: bool,

    #[bpaf(external)]
    command:HciCommand, 

}

And I get the following error

user@bluedev:~/usb/rust-usb-examples$ cargo build  --bin bluetooth_le_controller 
   Compiling rust-usb-examples v0.1.0 (/home/user/usb/rust-usb-examples)
error[E0277]: the trait bound `(): Parser<HciCommand>` is not satisfied
  --> src/bin/bluetooth_le_controller.rs:78:17
   |
78 | fn command() -> impl Parser<HciCommand> {    
   |                 ^^^^^^^^^^^^^^^^^^^^^^^ the trait `Parser<HciCommand>` is not implemented for `()`
   |
   = help: the following other types implement trait `Parser<T>`:
             <ParseAny<T> as Parser<T>>
             <ParseArgument<T> as Parser<T>>
             <ParseBox<T> as Parser<T>>
             <ParseCommand<T> as Parser<T>>
             <ParseCompShell<P> as Parser<T>>
             <ParseCon<P> as Parser<T>>
             <ParseMany<P> as Parser<Vec<T>>>
             <ParseOptional<P> as Parser<Option<T>>>
           and 18 others

For more information about this error, try `rustc --explain E0277`.
error: could not compile `rust-usb-examples` due to previous error

[pacak]

fn command() -> impl Parser<HciCommand> {    
    short('c')
    .long("command")
    .help("choose between hci_reset or hci_read_bd_addr")
    .argument::<HciCommand>("CMD")
    .to_options()
    .run();
}

Last two lines mean you want to try to execute your parser, ; means you return () which doesn't implement Parser, dropping last two lines might do the trick:

fn command() -> impl Parser<HciCommand> {    
    short('c')
    .long("command")
    .help("choose between hci_reset or hci_read_bd_addr")
    .argument::<HciCommand>("CMD")
}

external exists mostly to help to factor out parsers that have complex logic inside them, in this case it's a simple FromStr - no need to do that, bpaf would derive it automagically. I think same goes about reset if it's a simple bool

#[allow(dead_code)]
#[derive(Debug, Clone, Bpaf)]
#[bpaf(options)]
/// Example for bluetooth low energy controller demo
struct Options {
    #[bpaf(short, long, argument::<String>("DEVICE"), parse(parse_device))]
    /// [vendor]:[product] Open a device with the specified vendor and product ID.
    /// Both IDs are given in hexadecimal.
    device: (u16, u16),

    /// Increase verbosity
    #[bpaf(external)]
    verbose: usize,

    #[bpaf(short, long)]
    reset: bool,

    #[bpaf(short, long)]
    /// Choose between hci_reset or hci_read_bd_addr
    command: HciCommand, 
}

[potto216]

Thanks, changing command() worked

fn command() -> impl Parser<HciCommand> {    
    short('c')
    .long("command")
    .help("choose between hci_reset or hci_read_bd_addr")
    .argument::<HciCommand>("CMD")
}

How do you get the derive macro to pick up a help string. From the docs it looks like this should work:

    #[bpaf(short, long)]
    // Reset the USB device
    reset: bool,

But I cannot get it to.

[pacak]

How do you get the derive macro to pick up a help string. From the docs it looks like this should work: #[bpaf(short, long)] // Reset the USB device reset: bool, But I cannot get it to.

```rust // comment /// doc string ``` You need doc string.

[potto216]

Thanks!

    #[bpaf(short, long)]
    /// Reset the USB device
    reset: bool,

worked great